@moia-dev/bastion-host-forward

Bastion Host Forward

This CDK Library provides custom constructs BastionHostRDSForward and BastionHostRedisForward. It's an extension for the BastionHostLinux, which forwards traffic from an RDS Instance or Redis in the same VPC. This makes it possible to connect to a service inside a VPC from a developer machine outside of the VPC via the AWS Session Manager. The library allows connections to a basic-auth RDS via username and password or IAM, as well as to Redis clusters.

Setup

Instantiating the Bastion Host

Include this library into your project via npm

npm install @moia-dev/bastion-host-forward

A minimal example for creating the RDS Forward Construct, which will be used via username/password could look like this snippet:

import * as cdk from '@aws-cdk/core';
import * as ec2 from '@aws-cdk/aws-ec2';
import { BastionHostRDSForward } from '@moia-dev/bastion-host-rds-forward';

export class BastionHostPocStack extends cdk.Stack {
  constructor(scope: cdk.App, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    const vpc = ec2.Vpc.fromLookup(this, 'MyVpc', {
      vpcId: 'vpc-0123456789abcd'
    });

    const securityGroup = ec2.SecurityGroup.fromSecurityGroupId(
      this,
      'RDSSecurityGroup',
      'odsufa5addasdj',
      { mutable: false }
    );

    const rdsInstance = rds.DatabaseInstance.fromDatabaseInstanceAttributes(
      this,
      'MyDb',
      {
        instanceIdentifier: 'abcd1234geh',
        instanceEndpointAddress: 'abcd1234geh.ughia8asd.eu-central-1.rds.amazonaws.com',
        port: 5432,
        securityGroups: [securityGroup]
      }
    );

    new BastionHostRDSForward(this, 'BastionHost', {
      vpc: vpc,
      rdsInstance: rdsInstance,
      name: 'MyBastionHost',
    });

If the RDS is IAM Authenticated you also need to add an iam_user and rdsResourceIdentifier to the BastionHostRDSForward:

...
new BastionHostRDSForward(this, 'BastionHost', {
  vpc: vpc,
  rdsInstance: rdsInstance,
  name: 'MyBastionHost',
  iamUser: 'iamusername',
  rdsResourceIdentifier: 'db-ABCDEFGHIJKL123'
});

This will spawn a Bastion Host in the defined VPC. You also need to make sure that IPs from within the VPC are able to connect to the RDS Database. This needs to be set in the RDS's Security Group. Otherwise the Bastion Host can't connect to the RDS.

The instantiation of a BastionHostRedisForward works very similar to the RDS example, except that you pass a CfnCacheCluster to the BastionHost like this:

new BastionHostRedisForward(this, 'RedisBastion', {
  elasticacheCluster: cluster,
  vpc: vpc,
});

Install the Session-Manager Plugin for AWS-CLI

You are also able to connect to the Bastion Host via the AWS Web Console. For this go to AWS Systems Manager -> Session Manager -> choose the newly created instance -> click on start session.

But overall it's a much more comfortable experience to connect to the Bastion Session Manager Plugin. On Mac OSX you can get it via homebrew for example:

brew cask install session-manager-plugin

For Linux it should also be available in the respective package manager. Also have a look at the official installation instructions from AWS

Forward the connection to your machine

The Session Manager offers a command to forward a specific port. On the Bastion Host a HAProxy was installed which forwards the connection on the same port as the specified service. Those are by default:

• RDS: 5432
• Redis: 6739

In the following example, we show how to forward the connection of a PostgreSQL database. To forward the connection to our machine we execute the following command in the shell:

aws ssm start-session \
    --target <bastion-host-id> \
    --document-name AWS-StartPortForwardingSession \
    --parameters '{"portNumber": ["5432"], "localPortNumber":["5432"]}'

This creates a port forward session on the defined localPortNumber. The target is the id of the bastion host instance. This will be output automatically after deploying the bastion host. The portNumber must be the same as the RDS Port.

Now you would be able to connect to the RDS as it would run on localhost:5432.

Additional step if you are using IAM Authentication on RDS

If you have an IAM authenticated RDS, the inline policy of the bastion host will be equipped with access rights accordingly. Namely it will get rds:* permissions on the RDS you provided and it also allows rds-db:connect with the provided iamUser.

Most of the steps you would perform to connect to the RDS are the same, since it wouldn't be in a VPC.

First you generate the PGPASSWORD on your local machine:

export
PGPASSWORD="$(aws rds generate-db-auth-token
--hostname=<rds endpoint> --port=5432
--username=<iam user> --region <the region of the rds>)"

You also need to have the RDS certificate from AWS, which you can download:

wget https://s3.amazonaws.com/rds-downloads/rds-ca-2019-root.pem

There is now an additional step needed, because the certificate checks against the real endpoint name during the connect procedure. Therefore we need to add an entry to the /etc/hosts file on our machine:

echo "127.0.0.1  <rds endpoint>" >> /etc/hosts

Now you can connect to the IAM authenticated RDS like this:

psql "host=<rds endpoint> port=5432 dbname=<database name> user=<iamUser> sslrootcert=<full path to downloaded cert> sslmode=verify-ca"

For a full guide on how to connect to an IAM authenticated RDS check out this guide by AWS